Capacitive sensing is used in a wide range of applications. These applications include the sensing of substances such as gases, liquids, dusts, volatile substances and humidity. Other applications include pressure sensors, finger-print sensors, sensors for detecting spatial position, sensors for the detection of biomolecules (e.g. for biomarker detection).
In many applications, it is desirable to keep the size of the sensing circuitry as small as possible, so as to reduce costs. This can be a particular challenge in applications that require the use of multiple capacitive sensors on a single chip.
It is desirable to keep the amount of analogue circuitry included in the sensing circuitry to a minimum, so as to increase design flexibility, to improve the reliability of the sensor and to reduce the time to market. For instance, in case of some applications that include multiple capacitive sensors (e.g. a two-dimensional sensor array), the use of long wires for passing analogue signals from the sensors can degrade the integrity of the signals and can reduce sensitivity.
Various circuit topologies have been proposed for capacitance sensing. These generally include either analogue inputs/outputs, which require the use of long wires for passing analogue signals, which can degrade the quality of the sensed signal as noted above, or provide a digital implementation with poor sensitivity.